Thick film dielectric structures as exemplified by U.S. Pat. No. 5,432,015 (the entirety of which is incorporated herein by reference) are known and exhibit superior characteristics to that of traditional thin film electroluminescent (TFEL) displays. High performance red, green and blue phosphor materials have been developed for use with thick film dielectric structures to provide increased luminance performance. These phosphor materials include europium activated barium thioaluminate based materials for blue emission, terbium activated zinc sulfide, manganese activated magnesium zinc sulfide or europium activated calcium thioaluminate based materials for green emission, as well as traditional manganese activated zinc sulfide that can be appropriately filtered for red emission.
A high luminosity full colour thick film dielectric electroluminescent display requires that the thin film phosphor materials used for the red, green and blue sub-pixels be patterned so that the emission spectrum for each colour of pixel is tailored to minimize the attenuation associated with the optical filters needed to achieve the required colour coordinates for each sub-pixel. For relatively low-resolution displays patterning can be achieved by depositing the phosphor materials through a shadow mask. However, for high resolution displays the shadow mask technique does not provide adequate accuracy requiring that photolithographic methods be employed. Photolithographic techniques, as exemplified in U.S. patent application Ser. No. 09/540,288 (the entirety of which is incorporated herein by reference) require the deposition of photoresist films and the etching or lift-off of portions of the phosphor film to provide the required pattern. Deposition and removal of photoresist films and etching and or lift-off of phosphor films requires the use of solvent solutions that contain water or other protic solvents. Traces of these solutions remaining in the display structure following photolithographic processing together with reaction of moisture or oxygen present in the processing environment may react chemically with certain phosphor materials sensitive to oxidation or hydrolysis reactions to cause performance degradation of the completed display. Continued chemical reactions during operation of the display may cause continued performance degradation thereby shortening the life of the display.
To overcome such performance degradation problems, the use of various materials in conjunction with certain phosphor materials has been proposed. Silicon nitride has been proposed for use with terbium activated zinc sulfide and zinc magnesium sulfide phosphors (Mikami et al., 2000 Proceedings of the 6th International Conference on the Science and Technology of Display Phosphors; J. Ohwaki et al., 1987, Review of the Electrical Communications Laboratories Vol. 35).
U.S. Pat. Nos. 4,188,565, 4,721,631, 4,897,319 and 5,644,190 disclose the use of silicon nitride layers or silicon oxynitride layers in conjuction with a manganese activated zinc sulfide phosphor film using a plasma chemical vapour deposition method.
U.S. Pat. Nos. 5,496,597 and 5,598,059 disclose the use of aluminum oxide in conjunction with a terbium doped zinc sulfide for electroluminescent displays. WO 00/70917 discloses an electroluminescent laminate that includes a rare earth activated zinc sulfide material having a diffusion barrier layer of zinc sulfide.
Aluminum nitride has also been proposed for use with EL emitting layers of alkali earth chalcogen compounds in thin film electroluminescent devices as described in U.S. Pat. No. 4,975,338 and JP 02103893. Aluminum nitride has also been used as an insulating thin film layer in organic electroluminescent elements/displays as described in JP 08288069, JP 10092580, U.S. Pat. Nos. 6,146,225, 6,383,048 and 6,416,888 as well as a moisture barrier layer in EL elements as described in U.S. 2002/0079836 and U.S. 2002/0031688. Aluminum nitride as a ceramic substrate has also been proposed as disclosed in U.S. 2002/0177008.
U.S. 2002/0125821 discloses the use of aluminum nitride as a semiconductor material interposed between a conventional manganese activated zinc sulfide phosphor film and a thick film dielectric layer. The device is constructed by annealing the phosphor film, applying a layer of aluminum nitride on top of the annealed phosphor and then screen printing and sintering a thick film dielectric layer thereon such that the aluminum nitride is placed between the phosphor film and the thick film dielectric layer.
While the aforementioned patents and patent applications may teach the use of certain insulator materials such as aluminum nitride in conjunction with conventional zinc sulfide phosphors or within thin film electroluminescent displays, there remains a need to provide specific improved phosphor materials for use within thick film dielectric electroluminescent displays that exhibit improved luminance and a long operating life with minimal degradation.